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Collectable Minerals of the 
Terlingua Area

Oct 11 at 1:48 PM

COLLECTABLE MINERALS OF THE TERLINGUA AREA

Condensed from: 
Collectable Minerals of the Terlingua Cinnabar District and surrounding area.
Copyright 2013 by Fred Gossien
Due to be published December, 2013

1.  Cinnabar - Small specimen-grade cinnabar is still found in some mine  tailings.  Larger ore-grade pieces are very rare.  Large cinnabar  crystals, such as those currently coming from China, never existed in  the district.

2.  Terlingua Calcite - Terlingua Calcite is defined as that which  fluoresces a strong blue with exposure to shortwave ultraviolet light  (UV), with long-lasting phosphorescence, and under longwave UV  fluoresces pink without phosphorescence.  It is usually, but not always, pink in color and is a "must have" for fluorescent mineral collectors  worldwide.  Calcite not meeting the fluorescent/phosphorescent  definition would be called "calcite from Terlingua," not Terlingua  Calcite.  For more information go to http://www.terlinguacalcite.com/.

3.  Other calcites -  Calcite occurs in more crystal forms than any other  mineral, with a dozen or more found in the area (I've never counted).   Many of these are of sufficient size and quality for most mineral  collections.

4.  Fluorite -  Small fluorite cubes and plates of cubes are found near  several mines or prospects, rarely over about 1/4" on edge.  They are  mostly a muddy yellow color though some water clear and milky white  specimens occur.  Most rare are very tiny purple cubes found at a remote prospect.

5.  Quartz -  In the vicinity of cinnabar mines quartz crystals are  extremely rare.  A small number of tiny double-terminated crystals have  been found perched on calcite at only two locations, never associated  with either cinnabar or Terlingua Calcite.  Tiny bright green  fluorescing chalcedony balls (a form of quartz) are, however,  occasionally seen on the surface of Terlingua Calcite.  Quartz, calcite  and chalcedony geodes up to about a foot in diameter have been found in  some intrusions and lava flows in the area.  Some amethyst and slightly  smoky quartz have also been found.

6.  Opal -  Small chunks of common opal were found some 15-20 miles north  of the district, scattered over an area of about 1/2 square mile.  Most  are milky white but some are shades of blue, tan and grey.  Most of the  white pieces fluoresce bright green under shortwave UV due to trace  amounts of uranium.

7.  Analcime, natrolite and stilbite -  In late 2001 in a small pocket near the southwest fringe of the district notable crystals of these minerals were found.  Analcime (with an unmistakable 24-sided crystal structure) was known only to about 5 mm in diameter (about 3/16") while specimens  from the pocket exceeded 50 mm (over 2"); perfect natrolite crystals to  over 3" were found, far larger than was previously known, and stilbite,  previously unknown in the area, was found as 4-5 mm crystal clusters on, and in the matrix around, analcime crystals.

8.  Apophilite -  About a mile from the analcime site, masses of white  pseudo-rectangular crystals, individual crystals to nearly an inch, were found in vugs up to about 2 feet in diameter.  These were later  determined to be one of the three recognized varieties of apophilite,  the exact variety still unknown.

9.  Terlingua marbles -  These are the Terlingua equivalent to Utah's  famous Moqui marbles which are now illegal to collect.  They were found  scattered over a large area some 20 miles north of Terlingua and are  mostly limonite, not a distinct mineral but a term describing various  iron oxides of indefinite composition, resulting from altered pyrite.   The shiny black crystals on some marbles are probably specular hematite.

10.  Petrified wood -  More correctly called fossilized wood, it occurs  throughout the region, mostly in very scattered localized  concentrations.  It is commonly in rather drab shades of brown or grey  but colorful agatized pieces are sometimes found.  It can sometimes be  found in Terlingua Creek and Rough Run.

Note:  Several other minerals occur and are discussed in the complete text of  this publication, along with greatly expanded versions of the above  minerals. The additional minerals include barite, gypsum, aragonite,  garnet, pectolite, vanadinite and several iron oxides.

Caution:  Remember that all land in the region is private property except the  state and national parks (where collecting is illegal).  Get permission  before trespassing.  Also, rattlesnakes and dehydration are out there  waiting for you.  Be careful!  Use common sense!  Have fun!

 

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